Control units, whose computing elements are connected, via a transceiver, to a client-server network taking the form of a field bus, are conventional. The computing element may take the form of a microprocessor or a microcontroller. A computing element in the form of a finite state machine (so-called state machine) is also possible.
The network may have any topology; for example, a ring, a star, a line, or a tree topology is possible. The following types of field buses are considered, for example, as a client-server network. ARINC-629 (rapid avionics bus of the company Arinc, used in the Boeing 777, for example); AS interface for connecting sensors and actuators; CAN bus, used mainly in the automotive branch; EIB (electrical installation bus), used chiefly in building installation; FlexRay bus, used mainly in the automotive branch for X-by-wire systems; I2C; Interbus, used in machine construction or plant construction in a special design for safety engineering; LIN (local interconnect network) bus, used in the automotive branch; LON; Modbus; MOST bus, used in the automotive multimedia area; Profibus, used in robots, in machine construction, in plant construction, or in process automation; and Sercos, used in robots, in machine construction, and in plant construction.
For example, conventional LIN transceivers connect a computing element taking the form of a microprocessor or microcontroller to the data line of an LIN bus. Transmitted signals (Tx) and received signals (Rx) are exchanged by the transceiver and the computing element, in order to determine if the transceiver should transmit data through the LIN bus or receive data from the LIN bus.
During the testing and application phase of a control unit, it may be particularly important to monitor the state of the transmitted signal and received signal. In this manner, the functional sequences in the control unit and on the LIN bus may be more effectively monitored and, if necessary, corrected. When a HI voltage level applied to the LIN bus changes into a LO voltage level, it may be important to find out the reason for the change to the LO voltage level during the testing and application phase. For example, a change may be triggered by a switching element (e.g. a transistor) in the transceiver, the switching element being triggered by transmitted signal (Tx) and “pulling down” the HI voltage level to ground. During the testing and application phase, it may be important to find out whether the change to the LO voltage level was triggered by a monitored control unit or by a different control unit connected to the LIN bus. This may be ascertained by correlating the signal level on the data line of the LIN bus and transmitted and received signals (Tx, Rx) of the monitored control unit or the other control units.
Conventionally, in order to have knowledge of the current transmitted and received signals, the transmitted and received signals can be directed out to test terminals on the outside of the control-unit housing, where they can then be picked off and subsequently processed. However, this is only possible in control units in which the computing element and the transceiver are formed on separate chips, which means that the transmitted and received signals must be transmitted by lines between the two components, at which they can be easily picked off and directed outside. Even when the transceiver and the computing element take the form of separate components, this manner of rendering the transmitted and received signals accessible is relatively complicated and expensive. In addition, different control units must be provided with test terminals for transmitted and received signals (Tx, Rx) for the testing and application phase, and the different control units must not have such terminals for production applications.
In the past, there has been a tendency towards large-scale integrated semiconductors, which also had effects on the design and the manufacture of the computing-element/transceiver units in the control units. Thus, conventionally, for example, the computing element and the transceiver can be formed on a common, large-scale integrated chip, in which case instead of an expensive microcontroller, e.g., the computing element may take the form of a more simple and cost-effective finite-state machine (a so-called state machine). In the case of such large-scale integrated computing-element/transceiver units, transmitted signals (Tx) and received signals (Rx) travel in the interior of the chip and may no longer be picked off and directed to the outside of the control-unit housing, or may only be picked off and directed to the outside of the control-unit housing with a high degree of expenditure.